Method for identifying compounds for treatment of pain

ABSTRACT

Methods and products for the attenuation or treatment of pain and the reduction of nociception are described. The methods and products are based on the modulation of CNS intracellular chloride levels. The methods and products may also relate to modulation of the activity and/or expression of a chloride transporter, such as the KCC2 potassium-chloride cotransporter. Also described herein are commercial packages and uses based on such modulation. Related methods for identifying or characterizing a compound for the treatment of pain, the reduction of nociception and the diagnosis and prognostication of pain are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the 371 National Phase of International ApplicationNo. PCT/CA2004/000726, filed May 14, 2004, which was published inEnglish under PCT Article 21(2) as International Publication No. WO2004/101072. This application further claims the benefit, under 35U.S.C. §119(e), of U.S. provisional patent application Ser. No.60/470,885 filed May 16, 2003. All of these applications areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to the modulation of anion levels in a centralnervous system (CNS) neural cell, and particularly relates to themodulation of CNS intracellular chloride levels and uses thereof fortreating, preventing, diagnosing and prognosticating pain.

BACKGROUND OF THE INVENTION

The need for new and improved methods and agents for pain treatment is asignificant ongoing concern in medicine. Acute pain, e.g. related toinjury or disease, can be severe and have critical effects on patientrecovery. An even greater concern is chronic pain, which affects a largeproportion of the population, causing not only significant discomfort,but can result in low self-esteem, depression, anger, and can interferewith or completely prevent a sufferer from typical daily activities.

While a number of studies have been done in this area, many mechanismsand pathways involved in pain sensation remain poorly understood. As inthe case of the sensation of various stimuli, it has been suggested thatpain sensation is related to altered neuronal excitability.

Ion cotransport has in some cases been thought to play a role in theprocessing of certain stimuli. For example, Howard et al. (28) havedemonstrated that mice generated with a targeted deletion of the Slc12a6gene, which encodes the KCC3 exporter, exhibit features of agenisis ofthe corpus callosum, including a locomotor deficit, peripheralneuropathy and a sensorimotor gating deficit. Sung et al. (29) reportthat in mice where there is a disruption of the Slc12a2 gene, whichencodes the NKCC1 cotransporter, sensitivity to thermal stimulus isgreatly reduced, compared to both wild-type and heterozygous(NKCC1^(+/−)) mice.

There remains a need to better define the mechanisms involved in painsensation to provide new strategies of therapeutic intervention in thisregard.

SUMMARY OF THE INVENTION

This invention relates to pain and methods of treating, preventing,diagnosing and prognosticating such pain. This invention also relates topain associated with neuropathic pain and CNS dysfunction. Thisinvention also relates to methods of decreasing an intracellularchloride level in a central nervous system (CNS) neural cell.

According to one aspect, the invention provides a method of treating orpreventing pain in a subject, the method comprising decreasing anintracellular chloride level in a central nervous system (CNS) neuralcell of the subject. In an embodiment, the method comprises modulatingthe activity or expression of a chloride transporter in the CNS cell,thereby to decrease the chloride level. In a further embodiment, thechloride transporter is KCC2 the method comprises increasing KCC2activity or expression. In another embodiment, the CNS neural cell is aspinal cord neural cell. In yet another embodiment, the signal of thepain originates in a peripheral nervous system (PNS) cell or sensoryfiber transsynaptic to the CNS neural cell. In still another embodiment,the pain is neuropathic pain, and in further embodiments the neuropathicpain is associated with a nerve or tract injury or is selected from thegroup consisting of somatic and visceral pain. In yet anotherembodiment, the pain is selected from the group consisting of chronicinflammatory pain, pain associated with arthritis, fibromyalgia, backpain, cancer-associated pain, pain associated with digestive disease,pain associated with Crohn's disease, pain associated with autoimmunedisease, pain associated with endocrine disease, pain associated withdiabetic neuropathy, phantom limb pain, spontaneous pain, chronicpost-surgical pain, chronic temporomandibular pain, causalgia,post-herpetic neuralgia, AIDS-related pain, complex regional painsyndromes type I and II, trigeminal neuralgia, chronic back pain, painassociated with spinal cord injury and recurrent acute pain.

In an embodiment, the method comprises administering to the subject acompound capable of decreasing the intracellular chloride level in theCNS cell. In yet another embodiment, the compound is capable ofmodulating the activity or expression of a chloride transporter in theCNS cell. In yet a further embodiment, the chloride transporter is KCC2,and yet further, the compound is capable of increasing KCC2 activity orexpression. In another embodiment, the compound is an inhibitor of TrkB,such as K-252a or an anti-TrkB antibody. In another embodiment, thecompound is an inhibitor of cyclic AMP-dependent kinase (PKA) (e.g.H-89). In another embodiment, the compound is an inhibitor ofcalmodulin-dependant kinase (CAM kinase), and further, it is KN-93. Inan embodiment, KCC2 comprises an amino acid sequence substantiallyidentical to a sequence selected from the group consisting of SEQ ID NO:2, 4, 6 and a fragment thereof.

According to another aspect of the present invention, there is provideda composition for the treatment or the prevention of pain in a subject,the composition comprising a compound capable of decreasing anintracellular chloride level in a CNS neural cell; and apharmaceutically acceptable carrier. In an embodiment, the compound iscapable of modulating the activity or expression of a chloridetransporter in the CNS neural cell. In a further embodiment, thechloride transporter is KCC2, and further, the compound is capable ofincreasing KCC2 activity or expression.

According to still another aspect of the invention, there is provided acommercial package comprising the composition described herein togetherwith instructions for its use in the treatment or prevention of pain.

According to yet another aspect of the invention, there is provided acommercial package comprising a compound capable of decreasing anintracellular chloride level in a CNS neural cell together withinstructions for its use the treatment or prevention of pain. In anembodiment, the compound is capable of modulating the activity orexpression of a chloride transporter in said CNS neural cell. In afurther embodiment, the chloride transporter is KCC2, and further, thecompound is capable of increasing said KCC2 activity or expression.

According to a further aspect of the present invention, there isprovided use of the composition described herein for the treatment orprevention of pain and/or for the preparation of a medicament for thetreatment or prevention of pain.

According to yet a further aspect of the present invention, there isprovided use of a compound capable of decreasing an intracellularchloride level in a CNS neural cell for the treatment or prevention ofpain and/or for the preparation of a medicament for the treatment orprevention of pain. In an embodiment, the compound is capable ofmodulating the activity or expression of a chloride transporter in saidCNS cell. In a further embodiment, the chloride transporter is KCC2, andfurther, the compound is capable of increasing KCC2 activity orexpression. In another embodiment, the compound is an inhibitor of TrkB,and further, it is selected from the group consisting of K-252a and ananti-TrkB antibody. In another embodiment, the compound is an inhibitorof cyclic AMP-dependent kinase (PKA), and further, it is H-89. Inanother embodiment, the compound is an inhibitor of calmodulin-dependantkinase, and further, it is KN-93.

According to still a further aspect of the invention, there is provideda method of identifying or characterizing a compound for treatment orprevention of pain, the method comprising contacting a test compoundwith a CNS-derived cell; and determining whether the intracellularchloride level is decreased in the presence of the test compound;wherein the decrease is an indication that the test compound may be usedfor treatment or prevention of pain.

According to another aspect of the present invention, there is provideda method of identifying or characterizing a compound for treatment orprevention of pain, the method comprising contacting a test compoundwith a CNS-derived cell expressing a chloride transporter; anddetermining whether activity or expression of the chloride transporteris modulated in the presence of the test compound in such a way that thelevel intracellular chloride is decreased; wherein the modulation is anindication that the test compound may be used for treatment orprevention of pain. In an embodiment, the chloride transporter is KCC2,and further, the method comprises determining whether said KCC2expression or activity is increased in the presence of the test compoundand the modulation is an increase. In another embodiment, KCC2 activityis determined by measuring a parameter selected from the groupconsisting of potassium transport, chloride transport, intracellularchloride level and anion reversal potential. In still anotherembodiment, the pain is selected from the group consisting of chronicinflammatory pain, pain associated with arthritis, fibromyalgia, backpain, cancer-associated pain, pain associated with digestive disease,pain associated with Crohn's disease, pain associated with autoimmunedisease, pain associated with endocrine disease, pain associated withdiabetic neuropathy, phantom limb pain, spontaneous pain, chronicpost-surgical pain, chronic temporomandibular pain, causalgia,post-herpetic neuralgia, AIDS-related pain, complex regional painsyndromes type I and II, trigeminal neuralgia, chronic back pain, painassociated with spinal cord injury and recurrent acute pain.

According to yet another aspect of the present invention, there isprovided a method of identifying or characterizing a compound fortreatment or prevention of pain, said method comprising contacting atest compound with a CNS-derived cell comprising a first nucleic acidcomprising a transcriptionally regulatory element normally associatedwith a chloride transporter gene, operably linked to a second nucleicacid comprising a reporter gene capable of encoding a reporter protein;and determining whether reporter gene expression or reporter proteinactivity is modulated in the presence of the test compound; wherein themodulation in reporter gene expression or reporter protein activitybeing an indication that the test compound may be used for treatment orprevention of pain. In a further embodiment, the chloride transporter isKCC2, and further, the reporter gene expression or reporter proteinactivity is increased in the presence of the test compound.

According to one aspect of the present invention, there is provided amethod for decreasing nociception in a subject, the method comprisingdecreasing intracellular chloride in a CNS neural cell of the subject.In an embodiment, the method comprises modulating chloride transporteractivity or expression in the CNS neural cell. In a further embodiment,the chloride transporter is KCC2, and further, the method comprisesincreasing KCC2 activity or expression. In another embodiment, themethod further comprises contacting the CNS neural cell with a compoundcapable of increasing KCC2 activity or expression. In yet anotherembodiment, the compound is an inhibitor of TrkB, and further, it isselected from the group consisting of K-252a and an anti-TrkB antibody.In still another embodiment, the compound is an inhibitor of cyclicAMP-dependent kinase (PKA), and further, it is H-89. In yet anotherembodiment, the compound is an inhibitor of calmodulin-dependant kinase,and further, it is KN-93. In still another embodiment, KCC2 comprises anamino acid sequence substantially identical to a sequence selected fromthe group consisting of SEQ ID NO: 2, 4, 6 and a fragment thereof.

According to another aspect of the invention, there is provided a methodfor diagnosing or prognosticating pain associated with CNS dysfunctionin a subject experiencing pain, the method comprising determiningwhether a test CNS intracellular chloride level is increased relative toa corresponding control chloride level; wherein the increase is anindication that the subject is experiencing pain associated with CNSdysfunction. In an embodiment, the method further comprises determiningwhether CNS chloride transporter activity or expression is modulatedrelative to a control transporter activity or expression. In anotherembodiment, the chloride transporter is KCC2, and further, the methodcomprises determining whether KCC2 activity or expression is decreasedrelative to the control activity or expression. In still anotherembodiment, the control intracellular chloride level is selected fromthe group consisting of an established standard; a correspondingintracellular chloride level determined in the subject at an earliertime; a corresponding intracellular chloride level determined in thesubject when the subject is experiencing less pain or substantially nopain; and a corresponding intracellular chloride level determined in acontrol subject experiencing less pain or substantially no pain. In yetanother embodiment, the control activity or expression is selected fromthe group consisting of an established standard of KCC2 activity orexpression; a corresponding level of KCC2 activity or expressiondetermined in the subject at an earlier time; a corresponding level ofKCC2 activity or expression determined in the subject when the subjectis experiencing less pain or substantially no pain; and a correspondinglevel of KCC2 activity or expression determined in a control subjectexperiencing less pain or substantially no pain. In a furtherembodiment, KCC2 activity is determined by measuring a parameterselected from the group consisting of potassium transport, chloridetransport, intracellular chloride level and anion reversal potential. Instill a further embodiment, the intracellular chloride level isdetermined by administering an indicator compound indicative of chloridelevel to the subject such that it is contacted with a CNS neural cell ofthe subject; and assessing an in vivo signal associated with theindicator compound. In yet another embodiment, the pain associated withCNS dysfunction is neuropathic pain. In still yet another embodiment,the indicator compound is a radionuclide, and further, it is selectedfrom the group consisting of ²⁰¹Tl, ⁹⁹Tcm-tetrofosmin, ⁹⁹Tcm-MIBI,⁹⁹Tcm-HMPAO and ³⁶Cl. In still another embodiment, the in vivo signal isassessed by an imaging technique. In yet still another embodiment, thein vivo signal is the retention index of the indicator compound. In afurther embodiment, the imaging technique is selected from the groupconsisting of single photon emission computed tomography, positronemission tomography and magnetic resonance imaging. In yet a furtherembodiment, the indicator compound is indicative of KCC2 expression, andfurther, it is an antibody directed against KCC2.

According to yet another aspect of the invention, there is provided amethod of treating pain associated with CNS dysfunction in a subject,the method comprising diagnosing or prognosticating, according to themethods described herein, pain associated with CNS dysfunction in thesubject; and decreasing an intracellular chloride level in a CNS cell ofthe subject.

In an embodiment, the above-mentioned subject is a mammal, in a furtherembodiment, a human.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Peripheral nerve injury (PNI) induced a collapse of the∇_(anion) in Lamina I (LI) neurons in the ipsilateral superficial dorsalhorn (SDH). a) Chronic constriction injury of the sciatic nerve (n=23),but not sham surgery (n=11), caused a significant reduction in the 50%nociceptive withdrawal threshold to mechanical stimulation of thehindpaw in rats (p<0.01). b) Ranges of E_(anion) recorded from LIneurons of naïve (Δ) and PNI (∘) rats. Solid symbol=mean E_(anion)±SEM.c) All classes of LI neurons (i.e. with phasic (P), single-spike (SS)and tonic (T) firing properties [19]) showed a shift in E_(anion) inresponse to PNI. Scale bar is 50 mV (y), 150 ms (x). d) Mean peakcurrent measured in LI neurons from naïve (▴) and PNI (●) rats inresponse to applied GABA at various V_(m). Horizontal standard errorbars represent inter-neuron differences in recording pipette offset.Inset: Representative traces from one neuron. Scale bar is 0.6 nA (y),1.0 s (x).

FIG. 2: Switch from GlyR(receptor)-only to mixed GABA_(A)R- andGlyR-mediated miniature postsynaptic currents (mPSCs) following PNI inLI neurons. a) Raw traces of outward (left) and inward (right) miniaturesynaptic events from a naïve rat LI neuron. All outward mPSCs wereabolished by strychnine, while all inward mPSCs (recorded in thepresence of strychnine and bicuculline) were abolished by the GluRantagonist CNQX. HP—Holding Potential. Scale bar is 20 pA (y), 300 ms(x). b) Raw traces of inward (left) and outward (right) miniaturesynaptic events recorded from a PNI rat LI neuron. Unlike in naïve rats,both strychnine and bicuculline were required to abolish all outwardmPSCs. Inward mPSCs remained completely sensitive to CNQX. Scale bar is20 pA (y), 300 ms (x). c) left—Superimposed individual mPSCs recordedfrom PNI rat LI neurons. GlyR-only and GABA_(A)R-only and mixedGABA_(A)R/Glyr-mediated were clearly identifiable by their sensitivityto strychnine and/or bicuculline. Right—Averages of >100 GlyR- andGABA_(A)R-mediated mPSCs recorded from a PNI rat LI neuron. Scale bar is15 pA (y), 20 ms (x). d) Mean peak conductance of mPSCs recorded fromnaïve (N; n=10 for GlyR; n=5 for GluR) and PNI (P; n=9 for GlyR; n=8 forGluR) LI neurons. P(B) indicates GlyR-mediated mPSCs recorded in PNI ratLI neurons (n=12) at 0 mV in the presence of bicuculline. e) Net chargecarried by GlyR-mediated mPSCs in naïve rats (n=6), bybicuculline-isolated GlyR-mediated mPSCs in PNI rats [PNI(Bic); n=4],and by mixed GABA_(A)R/GlyR-mediated mPSCs in PNI rat LI neurons (PNI;n=12). f) Cumulative probability plot illustrating the differencebetween the GlyR-only mPSC inter-event interval (I.E.I.) in naïve LIneurons and that of bicuculline-isolated GlyR-only mPSCs in PNI rat LIneurons [PNI(Bic)], both recorded at E_(anion)=0 mV. The addition of theGABA_(A)R-mediated mPSCs (PNI) compensated the GlyR-only mPSC frequencydecrease. Inset—No effect of PNI on the frequency of GluR-mediatedmPSCs.

FIG. 3: PNI-induced downregulation of KCC2 in SDH lamina I neuronsipsilateral to PNI led to GlyR/GABA_(A)R-mediated excitation. a) BriefGABA application (30 ms pressure puff) caused a tetrodotoxin (TTX) andbicuculline-sensitive rise in [Ca²⁺]_(i) in a LI neuron from a fura-2-am(Ca²⁺ indicator) loaded slices of a PNI rat. b) KCl application, but notGABA application (up to 250 ms-long pressure puffs) caused no change in[Ca²⁺]_(i) in a naïve rat LI neuron. In the presence of theKCC2-specific antagonist DIOA, GABA application did elicit a rise in[Ca²⁺]_(i) in a naïve rat LI neuron. Scale bar is 0.02 (y), 10 s (x). c)Percentage of LI neurons displaying a GABA-evoked increase in[Ca²⁺]_(i). The proportion was significantly higher in PNI rats (χ²_(corrected)=3.91) and in the presence of DIOA in naïve rats (χ²_(corrected)=4.43). d) Representative trace confirming that exogenousGABA could repeatedly elicit action potentials in a lamina I neuron.Upper scale bar is 5 mV (y), 200 ms (x). Lower scale bar is 30 mV (y), 4s (x). Inset—response to a depolarizing pulse confirming this was asingle-spike neuron (19). Scale bar is 20 mV (y), 300 ms (x). e)Similarly, focal stimuli (in the presence of glutamate receptorblockers) elicited bicuculline-sensitive monosynaptic depolarizingpostsynaptic potentials thar could evoke action potentials in a lamina Ineuron from PNI rats. Scale bar is 5 mV (y), 250 ms (x). Inset—responseto a depolarizing pulse confirming this was a phasic neuron (19). Scalebar is 20 mV (y), 300 ms (x). f) Left—Immunoblotting revealed that KCC2levels were decreased in the lumbar SDH lying ipsilateral (Ipsi), butnot contralateral (Con), to the site of the PNI. Right—Averageintensities (±SEM) of KCC2 protein (normalized to actin) measured fromimmunoblots (n=4) as in left (Ipsi normalized to Con).

FIG. 4: Selective blockade or knock-down of the postsynaptic KCC2exporter in the SDH significantly reduced nociceptive threshold. a)Tactile nociceptive withdrawal threshold as a function of time afterintrathecal injections of DIOA (n=5) or vehicle (n=3). b) Thermalnociceptive withdrawal latency as a function of time after intrathecalinjections of DIOA (n=3) or vehicle (n=3). Upon withdrawal, the ratsalso often licked their paw indicating nociception. c) Spontaneous mPSCsrecorded with a CsCl (cesium chloride) pipette (to clamp E_(anion) at 0mV) in a LI neuron in the presence and absence of DIOA. Scale bar is 20pA (y), 300 ms (x). d) Cumulative probability plot (n=4 neurons×50mPSCs) demonstrating that DIOA neither affected the peak conductance ofsynaptic events (p>0.5), nor GABA-evoked responses (n=5; p>0.5, Inset)and therefore does not act on GlyRs nor GABA_(A)Rs. G_(peak)=peakconductance. e) Local lumbar spinal (intrathecal) administration of aKCC2 antisense oligodeoxynucleotide (each 12 h) caused a significantdecrease in the tactile nociceptive withdrawal threshold in naïve rats(n=8), compared to those that received the scrambledoligodeoxynucleotide (n=7). Inset, Decrease in spinal KCC2 proteinlevels (measured by immunoblots) following antisense (AS, 12 h or 36 h)or scrambled (S, 36 h) oligodeoxynucleotide treatment. f) Lack of KCC2immunoreactivity in dorsal root ganglia (DRG) in a naïve rat, comparedto SDH. g) Electron micrograph illustrating the selective expression ofKCC2 in SDH dendrites (D), but not synaptic boutons (B) (forquantitative details see FIG. 6). Arrows point to synapses. Scale bar is0.2 μm.

FIG. 5: Computer simulations of in vivo synaptic conditions confirmedthat sensitization of Lamina I neurons occurred as a function of theshift in the E_(anion). a) Left—Computer simulations using a modelneuron (see Examples) demonstrate how PNI-induced changes to GlyR- andGABA_(A)R-mediated PSCs [PNI(GlyR+GABA_(A)R)] affect the output firingfrequency of LI neurons as a function of GluR-mediated PSC frequency.Also shown is the result in LI neurons after PNI if only considering theeffect of GlyR- mediated [PNI(GlyR-only)] or GABA_(A)R-mediated[PNI(GABA_(A)R-only)] synaptic events. Right—Same data as shown in theleft panel, but expressed in terms of firing frequency ratio, which wascalculated as the quotient of a specific data set divided by the NoInhibition data set (i.e., a firing frequency ratio of one is equivalentto no inhibition). While the normally hyperpolarizing GlyR-mediated PSCs(mean E_(anion)=−72.8 mV in naïve rats) had a net inhibitory effect onthe output firing frequency (f_(out)), depolarizing GlyR-mediated PSCs(mean E_(anion)=−49.0 mV in PNI rats), enhanced f_(out) beyond thatpredicted to result with no inhibition, demonstrating a net excitatoryeffect. This excitatory effect was more prevalent when the GABA_(A)Rcomponent was incorporated due to the increased charge carried byGABA_(A)R-mediated PSCs. b) Left—Effect of different values of E_(anion)(over the range observed in our study) on the firing frequency of a LIneuron after PNI. Right—Same data as left panel expressed in terms offiring frequency ratio (as above).

FIG. 6: KCC2 exporter expression is restricted to dorsal horn neurons,not sensory fibres. Although the KCC2 levels are below detection byimmunoblotting from DRG (FIG. 4 f), we verified whether KCC2 could bepreferentially shuttled away from cell bodies to central terminals ofprimary afferents. a) Electron micrograph illustrating the presence ofKCC2 on dendrites (D) in lamina I of the dorsal horn. Membrane-delimitedimmunogold staining on the soma (S) of a lamina I neuron is also shown(arrowheads). In contrast, no KCC2 immunostaining was observed in any ofthe randomly selected synaptic profiles examined (n=171). b) KCC2immunoreactivity was also absent from central boutons (n=42 randomlyselected central boutons) of synaptic. glomeruli in laminae I and II(type I: C_(I); left; type II: C_(II); right; arrows indicate excitatorysynapses, D: dendrite) that unequivocally correspond to centralterminals of primary afferents (A- and C- fibres [34,35]). Scale bars:a: 2 μm; b; 0.5 μm (left), 0.2 μm (right).

FIG. 7: Effect of various treatments on anion (bicarbonate and chloride)reversal potential (E_(anion)) recorded from lamina I neurons of naïveand PNI rats.

FIG. 8: Intrathecal administration of the receptor tyrosine kinaseinhibitor K-252a (6 nM) resulted in an increase in the threshold fortactile nociceptive withdrawal.

FIG. 9: Polypeptide (SEQ ID NO: 2; FIG. 9A) and DNA (SEQ ID NO: 1; FIGS.9A-9C) sequences of human KCC2.

FIG. 10: Polypeptide (SEQ ID NO: 4; FIG. 10A) and DNA (SEQ ID NO: 3;FIGS. 10A-10B) sequences of mouse KCC2.

FIG. 11: Polypeptide (SEQ ID NO: 6; FIG. 11A) and DNA (SEQ ID NO: 5;FIGS. 11A-11C) sequences of rat KCC2.

FIG. 12: Comparison of the anion (chloride and bicarbonate) reversalpotential (E_(anion)) measured from lamina I neurons in slices, takenfrom naïve rats, perfused with BDNF, NGF or regular artificialcerebrospinal solution (ACSF; “control” in Figure). PNI—peripheral nerveinjury.

FIG. 13: Comparison of E_(anion) measured in slices containing lamina Ineurons taken from PNI rats treated, by bath application, with anantibody directed against TrkB (P/TrkBIgG), H-89 (P/H89), K-252a(P/K252a) and KN-93 (P/KN93). PNI—peripheral nerve injury.

FIG. 14: Comparison between the nociceptive threshold for tactilestimulation of rats treated with an adenovirus transducing BDNF (▪) andrats treated with an adenovirus transducing the green fluorescentprotein (◯).

FIG. 15: Comparison between the nociceptive threshold for tactilestimulation of rats treated with human recombinant NGF (10 μg/day×6days) (▪) and rats treated with saline vehicle (◯).

FIG. 16: Comparison between the nociceptive threshold for tactilestimulation of rats treated with the neutralizing anti-TrkB antibody(anti-TrkB-IgG 12 μg/2 hrs×3) (▪) and rats treated with vehicle only(◯).

FIG. 17: Comparison between the nociceptive threshold for mechanicalstimulation of rats treated with the PKA inhibitor H-89 (380 nmol) (▪)and rats treated with vehicle only (◯).

DETAILED DESCRIPTION OF THE INVENTION

Described herein is a novel mechanism of disinhibition followingperipheral nerve injury. It involves a transsynaptic disruption of anionhomeostasis in neurons of lamina I of the superficial dorsal horn (SDH),one of the main spinal nociceptive output pathways (7). The resultingshift in the transmembrane anion gradient is shown herein to causenormally inhibitory anionic synaptic currents to be excitatory,substantially driving up the net excitability of lamina I neurons. Asshown herein, peripheral nerve injury is sensed by transmission of asignal transynaptically resulting in an increase in intracellularchloride levels in central nervous system (CNS) neurons. Further, thestudies described herein demonstrate that decreasing CNS neuronalchloride levels can reverse this phenomenon, as shown via local blockadeor knock-down of the spinal KCC2 exporter in intact rats which markedlyreduced nociceptive threshold, confirming that the reported disruptionof anion homeostasis in lamina I neurons was sufficient to causeneuropathic pain.

Therefore, the studies described herein have investigated the mechanismof pain sensation via the study of downstream events followingperipheral nerve injury. As such, it is shown herein that such eventsare transmitted transsynaptically (e.g. by a peripheral nervous system(PNS cell or a sensory fiber) to central nervous system (CNS) neurons,in an embodiment, to spinal cord neurons. Further studies hereindemonstrate that transmission of the nociceptive signal and sensation ofpain is ultimately effected by a modulation of intracellular chloridelevel (e.g. modulated by a chloride transporter such as thepotassium-chloride cotransporter KCC2) in a CNS tissue. KCC2 (see (37)for a review) is a potassium-chloride cotransporter which has beenidentified in rat, mouse and human (for human KCC2 see for example U.S.Patent application Ser. No. 20030027983 of Mount et al.; published Feb.6, 2003). Studies of homozygous and heterozygous disruptions of the KCC2gene in mouse revealed a seizure phenotype, suggesting a possible rolefor KCC2 in epilepsy (38). The precise role of KCC2 in CNS function isnot yet completely understood.

Applicants demonstrate herein a correlation between the intracellularchloride level (e.g. by virtue of the activity/expression of a chloridetransporter such as KCC2) in a CNS cell or tissue, and the sensation ofpain. As shown in the examples below, peripheral nerve injury (PNI)results in the hyperexcitation or sensitization of CNS neurons, e.g. ofthe spinal cord, e.g. lamina I (LI) neurons of the superficial dorsalhorn (SDH). Such hyperexcitability occurs transsynaptically (i.e.downstream from the injured peripheral neuron), a phenomenon which hasnot been described prior to applicants' studies herein. Suchhyperexcitability results in a reduction of the nociceptive threshold.

As shown herein, the hyperexcitability noted above correlates with anincrease in intracellular chloride levels (e.g. modulation [e.g.decrease] in chloride transporter [such as KCC2] activity and/orexpression) in the SDH. The role of KCC2 in this regard was confirmedvia administration of the KCC2 blocker DIOA or a KCC2 antisenseoligonucleotide to spinal tissue, both resulting in a rapid decrease inthe threshold for pain sensitivity. Therefore, a reduction in KCC2activity and/or expression, if it results in increased CNS neuronalchloride levels, may result in a decrease in the threshold for painsensitivity, and, conversely, an increase or induction of KCC2 activityand/or expression, if it results in a decrease in CNS neuronal chloride,may result in an increase in the threshold for pain sensitivity thusproviding for prevention and treatment of pain. On the other hand, ithas been reported that under certain pathophysiological conditions, e.g.where [K⁺]_(o) is elevated, KCC2 may accumulate Cl⁻ in neurons, therebyenhancing neuronal excitability (42). Under such conditions, it isenvisioned that KCC2 would have the opposite effect on CNS neuronalchloride, and thus result in an increase in CNS neuronal chloride and inturn decreased nociceptive threshold and increased pain sensation. Assuch, modulation of the activity and/or expression of KCC2 may,depending on the directionality of the flux of chloride ion, contributeto or alleviate a pain sensation.

Therefore, in a first aspect, the invention relates to methods andmaterials for the treatment of pain, based on the modulation of CNSintracellular chloride level and further the modulation of the activityand/or expression of a chloride transporter, e.g. the KCC2potassium-chloride cotransporter. As used herein, a “chloridetransporter” is defined as a polypeptide/protein or complex thereofassociated with the cell membrane that is able to effect the passage ofchloride anions across the cell membrane. “Export(er)” refers to a netpassage from the inside to the outside of the cell, and “import(er)”refers to a net passage from the outside to the inside of the cell.

Therefore, in an embodiment, the present invention relates to methodsfor treating pain by decreasing the intracellular chloride level in acell, e.g. a CNS neural cell. In a further embodiment, modulators of achloride transporter (e.g. KCC2) can be used to decrease intracellularchloride levels. In an embodiment, the invention relates to theapplication, systemic or local, of compounds or drugs that decrease theintracellular level of chloride in a CNS neural cell as a means toattenuate pain. In order achieve this result, the above-mentionedcompounds or drugs may modulate the function or expression of thechloride transporter (e.g. KCC2 cotransporter) in CNS neurons. In yet afurther embodiment, the compounds or drugs may increase the expressionor activity of the chloride transporter or KCC2.

In an embodiment, the CNS neural cell in which the intracellularchloride levels are being modulated can be located in the superficialdorsal horn or the spinal cord. In addition, the cell may also betranssynaptic to a peripheral nerve cell or sensory fiber from which asignal for pain originates.

In an embodiment, the invention also relates to the treatment of acuteand chronic pain, more specifically to the treatment of neuropathicpain. “Neuropathic pain”, as used herein, refers to chronic painassociated with nerve injury (e.g. following crush, transection orcompression of nerves or following nerve degeneration resulting fromdisease). In an embodiment, neuropathic pain is associated with a nerveor tract injury. In a further embodiment, the neuropathic pain isassociated with visceral and/or somatic pain. The invention furtherrelates to decreasing CNS neuronal chloride levels (e.g. via modulationof chloride transporter [such as KCC2] activity and/or expression) toreduce nociception. “Nociception” as used herein refers to the sensorycomponent of pain. Pain may be the result of various stimuli, includingbut not limited to pressure, injury, thermal stimuli or chemical (e.g.ionic) stimuli. In embodiments, the pain may be associated with manyconditions such as chronic inflammatory pain, pain associated witharthritis, fibromyalgia, back pain, cancer-associated pain, painassociated with digestive disease, pain associated with Crohn's disease,pain associated with autoimmune disease, pain associated with endocrinedisease, pain associated with diabetic neuropathy, phantom limb pain,spontaneous pain, chronic post-surgical pain, chronic temporomandibularpain, causalgia, post-herpetic neuralgia, AIDS-related pain, complexregional pain syndromes type I and II, trigeminal neuralgia, chronicback pain, pain associated with spinal cord injury and/or recurrentacute pain. The invention also relates to methods of diagnosis andprognostication to assess pain associated with CNS dysfunction. In anembodiment, such diagnosis/prognostication may be performed prior to themethod of treatment described herein, or during a treatment regimen, tofurther characterize the nature of the pain or its progression, and thusprovide information which may be used e.g. to select a course oftreatment for such pain in accordance with the results obtained fromsuch diagnosis/prognostication. As used herein, “pain associated withCNS dysfunction” relates to a pain sensation that is caused by analteration in ion (e.g. anion) homeostasis in a CNS tissue. In anembodiment, the anion is a chloride ion. In a further embodiment, thealteration is an increase in an intracellular chloride level in a CNScell. In yet another embodiment, the activity or expression of achloride transporter may be modulated (e.g. KCC2 activity or expressionmay be modulated [e.g. decreased]) when a subject experiences painassociated with a CNS dysfunction.

“KCC2” as used herein refers to a particular type of potassium-chloridecotransporter expressed in neurons. In embodiments, KCC2 comprises thesequence of the polypeptide of SEQ ID NOs: 2 (human KCC2; see also FIG.9), 4 (mouse KCC2; see also FIG. 10) or 6 (rat KCC2; see also FIG. 11),fragments thereof or sequences substantially identical thereto. Infurther embodiments, KCC2 is encoded by the nucleic acid sequencescapable of encoding the polypeptides of SEQ ID NO: 2, 4 or 6, orfragments thereof or sequences substantially identical thereto orrelated by hybridization criteria (see below). In further embodiments,such nucleic acid sequences comprise of SEQ ID NO: 1 (human KCC2 DNA;see also FIG. 9), 3 (mouse KCC2 DNA; see also FIG. 10) or 5 (rat KCC2DNA; see also FIG. 11), fragments thereof or sequences substantiallyidentical thereto or related by hybridization criteria (see below).

“Chloride transport(er) activity” as used herein refers to the transportof chloride, across the cell membrane. Such transport activity may bemeasured by direct or indirect means using various methods known in theart, examples of which are described herein. “KCC2 activity” as usedherein refers to any detectable phenotype associated with KCC2. In anembodiment, KCC2 activity includes, but is not limited to potassiumtransport, chloride transport, which may, for example, be determined byassessing levels (either directly or indirectly) of potassium and/orchloride inside and/or outside the cell using, for example, reversalpotential measurements with patch clamping methods, chloride/potassiumsensitive dyes (see for example Haugland, R. P., Handbook of FluorescentProbes and Research Products, ninth ed., 2002, Molecular Probes, Inc.,Eugene, Oreg., USA) electrodes, etc. In addition, KCC2 activity may alsoaffect the neural cell's anion reversal potential (E_(anion)). The anionreversal potential may be determined, for example, by usinggramicidin-perforated patch clamp recording.

“Chloride transporter expression” (e.g. KCC2 expression) relates both toproduction of a chloride transporter transcript (e.g. a KCC2 transcript)or a chloride transporter polypeptide or protein (e.g. a KCC2polypeptide or protein). Chloride transporter expression (e.g. KCC2expression) may therefore, in embodiments, be determined by assessingprotein levels directly (e.g., by immunocytochemistry and/or westernanalysis) or a level of a chloride transporter-encoding nucleic acid(e.g. chloride transporter-encoding nucleic acid such as chloridetransporter mRNA levels) that may be determined by using, for example,methods such as reverse-transcriptase polymerase chain reaction [RT-PCR]methods, micro-array-based methods or by Northern analysis).

Compounds capable of decreasing intracellular chloride level in a CNSneural cell may, for example, modulate chloride transporter activity andexpression (e.g. KCC2 activity and expression). In an embodiment, thechloride transporter activity or expression (e.g. KCC2 activity orexpression) may be increased. In an embodiment, these compounds can beadministered in a way such that they contact a CNS tissue or a CNS cell.The compounds that can be used include, but are not limited to, thosewhich directly or indirectly modify the activity of the protein andthose which modulate the production and/or stability of the protein(e.g. at the level of transcription, translation, maturation,post-translationnal modification, phosphorylation and degradation).

One class of such compounds are those that act via modulation ofphosphorylation of one or more sites on KCC2. Upon cloning KCC2 (20), ithas been reported that KCC2 does not contain consensus phosphorylationsites for PKA, yet does contain five for PKC (Thr³⁴ , Ser⁷²⁸, Thr⁷⁸⁷,Ser⁹⁴⁰ & Ser¹⁰³⁴) One consensus site was identified for tyrosine proteinphosphorylation (Tyr¹⁰⁸¹) in the carboxyl-terminal. This tyrosine kinaseconsensus phosphorylation site is not present in the KCC1 or KCC4isoforms, yet it is conserved in the KCC3 protein (21). As such,compounds capable of upregulating or increasing KCC2 activity include,but are not limited to, protein kinases inhibitors (e.g.N-ethylmaleimide (23-25), staurosporine (29), and receptor tyrosinekinase inhibitors such as K-252a); antibodies or antibody fragmentsgenerated against certain kinases or kinase phosphorylation sites onKCC2, or compounds which interfere more directly (e.g. oligopeptidescapable of competing with phosphorylation sites on KCC2) or lessdirectly (e.g. compounds which modulate kinase activity and/orexpression) with KCC2 phosphorylation. In an embodiment, such a compoundmay act at the level of phosphorylation-mediated signaling pathways andultimately affect KCC2 phosphorylation. In another embodiment, TrkB maybe modulated to affect KCC2 phosphorylation and ultimately modulate KCC2activity. Thus, In an embodiment, compounds that inhibit TrkB activitymay, for example, be used in this regard. Such compounds may include,but are not limited to, K-252a (commercially available from Calbiochem)or a neutralizing antibody against TrkB (anti-TrkB antibody [e.g. IgG])(commercially available from BD Transduction Laboratories). In yetanother embodiment, modulation, e.g. inhibition, of cyclic AMP-dependantkinase or PKA may be useful in modulating KCC2 phosphorylation andultimately be used in the treatment or prevention of pain. For example,the PKA inhibitor H-89 (commercially available from EMD Biosciences) maybe used in this regard. In a further embodiment, modulation, e.g.inhibition, of calmodulin-dependant kinase (CAM kinase, e.g. II and IV)may alleviate or prevent pain in a subject by modulating KCC2 activity,e.g. phosphorylation. Compounds capable of inhibiting such a kinaseinclude, but are not limited to, KN-93 (commercially available from EMDBiosciences). In yet another embodiment, modulators, e.g. inhibitors, ofother members of the TrkB pathway, e.g. phosphatidylinositol-specificphospholipase C or phosphatidylcholine-specific phospholipase C, e.g.phospholipase C gamma (PLCγ), may be used to decrease intracellularchloride levels in a CNS neural cell. Such compounds include, but arenot limited to, tricyclodecan-9-yl-xanthogenate,1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphorylcholine, neomycinsulfate, spermine tetrahydrochloride,1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione,or1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-2,5-pyrrolidinedione.

Further, modulation of KCC2 expression may also arise from modulation(e.g. mediated by phosphorylation) of transcription factors whichregulate KCC2 expression. In a further aspect, the invention provides amethod for treating pain or preventing/decreasing nociception in asubject or animal, comprising modulating, in embodiments reducing ordecreasing, intracellular chloride levels in a CNS neuron or tissue. Inan embodiment, such decrease in intracellular chloride levels isachieved by modulating, e.g. decreasing, activity or expression of achloride transporter (e.g. KCC2) in a CNS neuron or tissue of thesubject. In a further embodiment, the subject is a vertebrate. Inanother embodiment, the subject is a mammal, in a yet furtherembodiment, a human. In an embodiment, the CNS tissue is spinal cordtissue and the neural cell is a spinal cord neural cell.

Accordingly, the invention therefore provides methods of treating paincomprising administering a compound capable of modulating, in anembodiment, decreasing or reducing intracellular chloride levels in CNStissue (e.g. a CNS neural cell) in a subject. In an embodiment, themodulation, e.g. increase, in chloride transporter (e.g. KCC2) activityand/or expression effects the decrease in intracellular chloride levelin the subject. In an embodiment, the CNS tissue is spinal cord tissueand the neural cell is a spinal cord neural cell.

In an embodiment, KCC2 comprises an amino acid sequence substantiallyidentical to a sequence set forth in SEQ ID NO: 2, 4, 6 or a fragmentthereof. In another embodiment, KCC2 may be encoded by a nucleic acidsubstantially identical to a nucleotide sequence capable of encoding SEQID NO: 2, 4, 6 or a fragment thereof, such as a sequence substantiallyidentical to the sequence set forth in SEQ ID NO: 1, 3, 5 or a fragmentthereof.

As noted above, a homolog, variant and/or fragment of a KCC2 whichretains activity may also be used in the methods of the invention.Homologs include protein sequences which are substantially identical tothe amino acid sequence of a KCC2, sharing significant structural andfunctional homology with a KCC2. Variants include, but are not limitedto, proteins or peptides which differ from a KCC2 by any modifications,and/or amino acid substitutions, deletions or additions. Modificationscan occur anywhere including the polypeptide backbone, (i.e. the aminoacid sequence), the amino acid side chains and the amino or carboxytermini. Such substitutions, deletions or additions may involve one ormore amino acids. Fragments include a fragment or a portion of a KCC2 ora fragment or a portion of a homolog or variant of a KCC2.

With regard to increasing or upregulating expression of KCC2 in a cell,various methods of introducing KCC2-encoding nucleic acids into the cellmay be used, examples of which are described below. Methods such as thegene therapy methods discussed below may be used in this regard.Examples of KCC2-encoding nucleic acids include nucleic acids capable ofencoding a polypeptide of SEQ ID NO: 2, 4 or 6 (e.g. the nucleic acidsof SEQ ID NO: 1, 3 and 5), or nucleic acids substantially identicalthereto. The method may also comprise administering to an area or neuraltissue, e.g. CNS tissue, a cell comprising such a KCC2-encoding nucleicacid, via for example transplantation or introduction of a neural cellor precursor thereto (e.g. a stem cell) comprising such a KCC2-encodingnucleic acid. Further, the method may entail administering to thesubject a compound capable of modulating, e.g. unpregulating orincreasing, expression of a KCC2. Such a compound may for example beidentified and characterized by the screening methods described below.Such a compound may further be provided as a composition comprising thecompound and a pharmaceutically acceptable carrier. In an embodiment,the composition is formulated for or adapted for administration to theCNS. Such a compound or composition may be provided in a commercialpackage together with instructions for its use.

“Homology” and “homologous” refers to sequence similarity between twopeptides or two nucleic acid molecules. Homology can be determined bycomparing each position in the aligned sequences. A degree of homologybetween nucleic acid or between amino acid sequences is a function ofthe number of identical or matching nucleotides or amino acids atpositions shared by the sequences. As the term is used herein, a nucleicacid sequence is “homologous” to another sequence if the two sequencesare substantially identical and the functional activity of the sequencesis conserved (as used herein, the term “homologous” does not inferevolutionary relatedness). Two nucleic acid sequences are consideredsubstantially identical if, when optimally aligned (with gapspermitted), they share at least about 50% sequence similarity oridentity, or if the sequences share defined functional motifs. Inalternative embodiments, sequence similarity in optimally alignedsubstantially identical sequences may be at least 60%, 70%, 75%, 80%,85%, 90% or 95%. As used herein, a given percentage of homology betweensequences denotes the degree of sequence identity in optimally alignedsequences. An “unrelated” or “non-homologous” sequence shares less than40% identity, though preferably less than about 25% identity, with anyof SEQ ID NO: 1 to 6.

Substantially complementary nucleic acids are nucleic acids in which the“complement” of one molecule is substantially identical to the othermolecule. Optimal alignment of sequences for comparisons of identity maybe conducted using a variety of algorithms, such as the local homologyalgorithm of Smith and Waterman, 1981, Adv. Appl. Math 2: 482, thehomology alignment algorithm of Needleman and Wunsch, 1970, J. Mol.Biol. 48:443, the search for similarity method of Pearson and Lipman,1988, Proc. Natl. Acad. Sci. USA 85: 2444, and the computerisedimplementations of these algorithms (such as GAP, BESTFIT, FASTA andTFASTA in the Wisconsin Genetics Software Package, Genetics ComputerGroup, Madison, Wis., U.S.A.). Sequence identity may also be determinedusing the BLAST algorithm, described in Altschul et al., 1990, J. Mol.Biol. 215:403-10 (using the published default settings). Software forperforming BLAST analysis may be available through the National Centerfor Biotechnology Information (through the internet athttp://www.ncbi.nlm.nih.gov/). The BLAST algorithm involves firstidentifying high scoring sequence pairs (HSPs) by identifying shortwords of length W in the query sequence that either match or satisfysome positive-valued threshold score T when aligned with a word of thesame length in a database sequence. T is referred to as theneighbourhood word score threshold. Initial neighbourhood word hits actas seeds for initiating searches to find longer HSPs. The word hits areextended in both directions along each sequence for as far as thecumulative alignment score can be increased.

Extension of the word hits in each direction is halted when thefollowing parameters are met: the cumulative alignment score falls offby the quantity X from its maximum achieved value; the cumulative scoregoes to zero or below, due to the accumulation of one or morenegative-scoring residue alignments; or the end of either sequence isreached. The BLAST algorithm parameters W, T and X determine thesensitivity and speed of the alignment. The BLAST program may use asdefaults a word length (W) of 11, the BLOSUM62 scoring matrix (Henikoffand Henikoff, 1992, Proc. Natl. Acad. Sci. USA 89: 10915-10919)alignments (B) of 50, expectation (E) of 10 (or 1 or 0.1 or 0.01 or0.001 or 0.0001), M=5, N=4, and a comparison of both strands. Onemeasure of the statistical similarity between two sequences using theBLAST algorithm is the smallest sum probability (P(N)), which providesan indication of the probability by which a match between two nucleotideor amino acid sequences would occur by chance. In alternativeembodiments of the invention, nucleotide or amino acid sequences areconsidered substantially identical if the smallest sum probability in acomparison of the test sequences is less than about 1, preferably lessthan about 0.1, more preferably less than about 0.01, and mostpreferably less than about 0.001.

An alternative indication that two nucleic acid sequences aresubstantially complementary is that the two sequences hybridize to eachother under moderately stringent, or preferably stringent, conditions.Hybridization to filter-bound sequences under moderately stringentconditions may, for example, be performed in 0.5 M NaHPO₄, 7% sodiumdodecyl sulfate (SDS), 1 mM EDTA at 65° C., and washing in 0.2×SSC/0.1%SDS at 42° C. (see Ausubel, et al. (eds), 1989, Current Protocols inMolecular Biology, Vol. 1, Green Publishing Associates, Inc., and JohnWiley & Sons, Inc., New York, at p. 2.10.3). Alternatively,hybridization to filter-bound sequences under stringent conditions may,for example, be performed in 0.5 M NaHPO₄, 7% SDS, 1 mM EDTA at 65° C.,and washing in 0.1×SSC/0.1% SDS at 68° C. (see Ausubel, et al. (eds),1989, supra). Hybridization conditions may be modified in accordancewith known methods depending on the sequence of interest (see Tijssen,1993, Laboratory Techniques in Biochemistry and MolecularBiology—Hybridization with Nucleic Acid Probes, Part I, Chapter 2“Overview of principles of hybridization and the strategy of nucleicacid probe assays”, Elsevier, N.Y.). Generally, stringent conditions areselected to be about 5° C. lower than the thermal melting point for thespecific sequence at a defined ionic strength and pH.

According to a further aspect, the invention also provides a method fordecreasing nociception in a subject. In an embodiment, this methodcomprises modulating, e.g. decreasing, intracellular chloride levels ina cell, e.g. a CNS cell, in a subject. In a further embodiment, themethod also comprises modulating, e.g. increasing, chloride transporteractivity or expression, e.g. KCC2 activity or expression. In yet anotherembodiment, the method also comprises contacting the CNS neural cellwith a compound capable of modulating chloride transporter activity.Such compounds include, but are not limited to a TrkB inhibitor (such asK-252a or anti-TrkB antibody), a PKA inhibitor (such as H-89) or a CAMkinase inhibitor (such as KN-93).

The invention further provides a composition for the prevention and/ortreatment of pain comprising a compound capable of modulating, e.g.decreasing, intracellular chloride levels in admixture with apharmaceutically acceptable carrier. In an embodiment, such compositionmay modulate, e.g. increase or upregulate, chloride transporteractivity, e.g. KCC2, activity and/or expression. In an embodiment, sucha composition is suitable for or adapted for administration to a CNSneural cell or tissue, such as spinal cord tissue or cell. In yet afurther embodiment, such a composition may be an inducer of KCC2expression or activity. As used herein, an “inducer” is a compound thatupregulates or enhances directly or indirectly the expression of theKCC2 gene, stability of the KCC2 mRNA, translation of the KCC2 mRNA,maturation of the KCC2 polypeptide, transport, e.g. recycling, of theKCC2 polypeptide to the cell membrane, or transporter activity of theKCC2 polypeptide. In an embodiment, the “inducer” can also down-regulateor inhibit KCC2 inhibitors.

The invention further provides a use of the above-mentioned compositionor the above-mentioned compound, capable of modulating, e.g. decreasing,intracellular chloride levels for the treatment or prevention of pain.The invention also provides a use of the above-mentioned composition orthe above-mentioned compound, capable of modulating, e.g. decreasing,intracellular chloride levels for the preparation of a medicament fortreatment or prevention of pain. In an embodiment, the compound orcomposition modulates, e.g. increases or upregulates, chloridetransporter (e.g. KCC2) activity and/or expression. In yet anotherembodiment, the compound or composition may comprise a TrkB inhibitor(such as K-252a or anti-TrkB antibody), a PKA inhibitor (such as H-89)or a CAM kinase inhibitor (such as KN-93). In yet another embodiment,the medicament may be formulated for administration to a CNS tissue,e.g. CNS cell, of a subject. Further, the compound may be, for example,an inducer of KCC2 expression or activity.

The invention further provides commercial packages comprising a compoundcapable of modulating, e.g. decreasing, intracellular chloride levels orthe above-described composition together with instructions for its usein the treatment or prevention of pain. In an embodiment, the compoundmay modulate, e.g. increase or upregulate, chloride transporter or KCC2activity and/or expression.

In various embodiments, a compound capable of modulating, e.g.decreasing, intracellular chloride levels in a CNS cell may be usedtherapeutically in formulations or medicaments to treat pain. Thecompound may, for example, modulate, e.g. increase or upregulatechloride transporter (e.g. KCC2) activity and/or expression. Theinvention also provides corresponding methods of medical treatment, inwhich a therapeutic dose of a compound capable of modulating, in anembodiment decreasing, intracellular chloride levels, is administered ina pharmacologically acceptable formulation. Accordingly, the inventionalso provides therapeutic compositions comprising a compound capable ofmodulating, in an embodiment decreasing intracellular chloride levels,and a pharmacologically acceptable excipient or carrier. The therapeuticcomposition may be soluble in an aqueous solution at a physiologicallyacceptable pH.

In an embodiment, a compound of the invention is administered such thatit comes into contact with a CNS tissue or a CNS neuron. As used herein,the “central nervous system” or CNS is the portion of the nervous systemcomprising the brain and the spinal cord (e.g. in the lumbar region). Bycontrast, the “peripheral nervous system” or PNS is the portion of thenervous system other than the brain and the spinal cord. In anembodiment, the CNS tissue is the superficial dorsal horn, in a furtherembodiment, a lamina I neuron. As such, in embodiments a compound of theinvention can be administered to treat CNS cells in vivo via directintracranial or intrathecal injection or injection into thecerebrospinal fluid. Alternatively, the compound can be administeredsystemically (e.g. intravenously, or orally) in a form capable ofcrossing the blood brain barrier and entering the CNS. “Neural” and“neuronal” are used herein interchangeably and both relate to neuronsand the nervous system.

The invention also provides pharmaceutical compositions (medicaments)comprising a compound capable of modulating, in an embodiment decreasingintracellular chloride levels in a CNS cell. In an embodiment, suchcompositions include the compound, in a therapeutically orprophylactically effective amount sufficient to treat or attenuate pain,and a pharmaceutically acceptable carrier. A “therapeutically effectiveamount” refers to an amount effective, at dosages and for periods oftime necessary, to achieve the desired therapeutic result, such asreduction of pain. A therapeutically effective amount of a compoundcapable of modulating, in an embodiment decreasing, intracellularchloride levels in a CNS cell, may vary according to factors such as thedisease state, age, sex, and weight of the individual, and the abilityof the compound to elicit a desired response in the individual. Dosageregimens may be adjusted to provide the optimum therapeutic response. Atherapeutically effective amount is also one in which any toxic ordetrimental effects of the compound are outweighed by thetherapeutically beneficial effects. A “prophylactically effectiveamount” refers to an amount effective, at dosages and for periods oftime necessary, to achieve the desired prophylactic result, such aspreventing or inhibiting onset of pain or increases in the severity ofpain. A prophylactically effective amount can be determined as describedabove for the therapeutically effective amount. For any particularsubject, specific dosage regimens may be adjusted over time according tothe individual need and the professional judgement of the personadministering or supervising the administration of the compositions.

As used herein “pharmaceutically acceptable carrier” or “excipient”includes any and all solvents, dispersion media, coatings, antibacterialand antifungal agents, isotonic and absorption delaying agents, and thelike that are physiologically compatible. In one embodiment, the carrieris suitable for parenteral administration. Alternatively, the carriercan be suitable for intravenous, intraperitoneal, intramuscular,intracranial, intrathecal, sublingual or oral administration.Pharmaceutically acceptable carriers include sterile aqueous solutionsor dispersions and sterile powders for the extemporaneous preparation ofsterile injectable solutions or dispersion. The use of such media andagents for pharmaceutically active substances is well known in the art.Except insofar as any conventional media or agent is incompatible withthe active compound, use thereof in the pharmaceutical compositions ofthe invention is contemplated. Supplementary active compounds can alsobe incorporated into the compositions.

Therapeutic compositions typically must be sterile and stable under theconditions of manufacture and storage. The composition can be formulatedas a solution, microemulsion, liposome, or other ordered structuresuitable to high drug concentration. The carrier can be a solvent ordispersion medium containing, for example, water, ethanol, polyol (forexample, glycerol, propylene glycol, and liquid polyethylene glycol, andthe like), and suitable mixtures thereof. The proper fluidity can bemaintained, for example, by the use of a coating such as lecithin, bythe maintenance of the required particle size in the case of dispersionand by the use of surfactants. In many cases, it will be preferable toinclude isotonic agents, for example, sugars, polyalcohols such asmannitol, sorbitol, or sodium chloride in the composition. Prolongedabsorption of the injectable compositions can be brought about byincluding in the composition an agent which delays absorption, forexample, monostearate salts and gelatin. Moreover, the compound capableof modulating, in an embodiment increasing or upregulating, KCC2activity and/or expression, can be administered in a time releaseformulation, for example in a composition which includes a slow releasepolymer. The active compounds can be prepared with carriers that willprotect the compound against rapid release, such as a controlled releaseformulation, including implants and microencapsulated delivery systems.Biodegradable, biocompatible polymers can be used, such as ethylenevinyl acetate, polyanhydrides, polyglycolic acid, collagen,polyorthoesters, polylactic acid and polylactic, polyglycolic copolymers(PLG). Many methods for the preparation of such formulations arepatented or generally known to those skilled in the art.

Sterile injectable solutions can be prepared by incorporating the activecompound (e.g. a compound capable of modulating, in an embodimentdecreasing, intracellular chloride levels in a CNS cell) in the requiredamount in an appropriate solvent with one or a combination ofingredients enumerated above, as required, followed by filteredsterilization. Generally, dispersions are prepared by incorporating theactive compound into a sterile vehicle which contains a basic dispersionmedium and the required other ingredients from those enumerated above.In the case of sterile powders for the preparation of sterile injectablesolutions, the preferred methods of preparation are vacuum drying andfreeze-drying which yields a powder of the active ingredient plus anyadditional desired ingredient from a previously sterile-filteredsolution thereof. In accordance with an alternative aspect of theinvention, a compound capable of modulating, in an embodimentdecreasing, intracellular chloride levels in a CNS cell, may beformulated with one or more additional compounds that enhance itssolubility.

In accordance with another aspect of the invention, therapeuticcompositions of the present invention, comprising a compound capable ofmodulating, in an embodiment decreasing, intracellular chloride levelsin a CNS cell, may be provided in containers or commercial packageswhich further comprise instructions for their use for the treatment ofpain.

Given that a decreased intracellular chloride level in a cell isassociated with a modulation, e.g. an increase, in level/activity ofchloride transporter (KCC2), which further correlates with a decrease inpain sensation as described herein, a further aspect of the presentinvention is the treatment of pain by administering to a subject (e.g.to CNS tissue) a nucleic acid molecule encoding a KCC2, or a variant orfragment thereof which retains KCC2 activity. Suitable methods ofadministration include gene therapy methods.

A nucleic acid of the invention may be delivered to cells in vivo usingmethods such as direct injection of DNA, receptor-mediated DNA uptake,viral-mediated transfection or non-viral transfection and lipid basedtransfection, all of which may involve the use of gene therapy vectors.Direct injection has been used to introduce naked DNA into cells in vivo(see e.g., Acsadi et al. (1991) Nature 332:815-818; Wolff et al. (1990)Science 247:1465-1468). A delivery apparatus (e.g., a “gene gun”) forinjecting DNA into cells in vivo may be used. Such an apparatus may becommercially available (e.g., from BioRad). Naked DNA may also beintroduced into cells by complexing the DNA to a cation, such aspolylysine, which is coupled to a ligand for a cell-surface receptor(see for example Wu, G. and Wu, C. H. (1988) J. Biol. Chem. 263:14621;Wilson et al. (1992) J. Biol. Chem. 267:963-967; and U.S. Pat. No.5,166,320). Binding of the DNA-ligand complex to the receptor mayfacilitate uptake of the DNA by receptor-mediated endocytosis. ADNA-ligand complex linked to adenovirus capsids which disrupt endosomes,thereby releasing material into the cytoplasm, may be used to avoiddegradation of the complex by intracellular lysosomes (see for exampleCuriel et al. (1991) Proc. Natl. Acad. Sci. USA 88:8850; Cristiano etal. (1993) Proc. Natl. Acad. Sci. USA 90:2122-2126). Defectiveretroviruses are well characterized for use as gene therapy vectors (fora review see Miller, A. D. (1990) Blood 76:271). Protocols for producingrecombinant retroviruses and for infecting cells in vitro or in vivowith such viruses can be found in Current Protocols in MolecularBiology, Ausubel, F. M. et al. (eds.) Greene Publishing Associates,(1989), Sections 9.10-9.14 and other standard laboratory manuals.Examples of suitable retroviruses include pLJ, pZIP, pWE and pEM whichare well known to those skilled in the art. Examples of suitablepackaging virus lines include .psi.Crip, .psi.Cre, .psi.2 and .psi.Am.Retroviruses have been used to introduce a variety of genes into manydifferent cell types, including epithelial cells, endothelial cells,lymphocytes, myoblasts, hepatocytes, bone marrow cells, in vitro and/orin vivo (see for example Eglitis, et al. (1985) Science 230:1395-1398;Danos and Mulligan (1988) Proc. Natl. Acad. Sci. USA 85:6460-6464;Wilson et al. (1988) Proc. Natl. Acad. Sci. USA 85:3014-3018; Armentanoet al. (1990) Proc. Natl. Acad. Sci. USA 87:6141-6145; Huber et al.(1991) Proc. Natl. Acad. Sci. USA 88:8039-8043; Ferry et al. (1991)Proc. Natl. Acad. Sci. USA 88:8377-8381; Chowdhury et al. (1991) Science254:1802-1805; van Beusechem et al. (1992) Proc. Natl. Acad. Sci. USA89:7640-7644; Kay et al. (1992) Human Gene Therapy 3:641-647; Dai et al.(1992) Proc. Natl. Acad. Sci. USA 89:10892-10895; Hwu et al. (1993) J.Immunol. 150:4104-4115; U.S. Pat. No. 4,868,116; U.S. Pat. No.4,980,286; PCT Application WO 89/07136; PCT Application WO 89/02468; PCTApplication WO 89/05345; and PCT Application WO 92/07573).

For use as a gene therapy vector, the genome of an adenovirus may bemanipulated so that it encodes and expresses a polypeptide compound ofthe invention, but is inactivated in terms of its ability to replicatein a normal lytic viral life cycle. See for example Berkner et al.(1988) BioTechniques 6:616; Rosenfeld et al. (1991) Science 252:431-434;and Rosenfeld et al. (1992) Cell 68:143-155. Suitable adenoviral vectorsderived from the adenovirus strain Ad type 5 dl324 or other strains ofadenovirus (e.g., Ad2, Ad3, Ad7 etc.) are well known to those skilled inthe art. Recombinant adenoviruses are advantageous in that they do notrequire dividing cells to be effective gene delivery vehicles and can beused to infect a wide variety of cell types, including airway epithelium(Rosenfeld et al. (1992) cited supra), endothelial cells (Lemarchand etal. (1992) Proc. Natl. Acad. Sci. USA 89:6482-6486), hepatocytes (Herzand Gerard (1993) Proc. Natl. Acad. Sci. USA 90:2812-2816) and musclecells (Quantin et al. (1992) Proc. Natl. Acad. Sci. USA 89:2581-2584).

Adeno-associated virus (AAV) may be used as a gene therapy vector fordelivery of DNA for gene therapy purposes. AAV is a naturally occurringdefective virus that requires another virus, such as an adenovirus or aherpes virus, as a helper virus for efficient replication and aproductive life cycle (Muzyczka et al. Curr. Topics in Micro. andImmunol. (1992) 158:97-129). AAV may be used to integrate DNA intonon-dividing cells (see for example Flotte et al. (1992) Am. J. Respir.Cell. Mol. Biol. 7:349-356; Samulski et al. (1989) J. Virol.63:3822-3828; and McLaughlin et al. (1989) J. Virol. 62:1963-1973). AnAAV vector such as that described in Tratschin et al. (1985) Mol. Cell.Biol. 5:3251-3260 may be used to introduce DNA into cells (see forexample Hermonat et al. (1984) Proc. Natl. Acad. Sci. USA 81:6466-6470;Tratschin et al. (1985) Mol. Cell. Biol. 4:2072-2081; Wondisford et al.(1988) Mol. Endocrinol. 2:32-39; Tratschin et al. (1984) J. Virol.51:611-619; and Flotte et al. (1993) J. Biol. Chem. 268:3781-3790).Lentiviral gene therapy vectors may also be adapted for use in theinvention.

General methods for gene therapy are known in the art. See for example,U.S. Pat. No. 5,399,346 by Anderson et al. A biocompatible capsule fordelivering genetic material is described in PCT Publication WO 95/05452by Baetge et al. Methods of gene transfer into hematopoietic cells havealso previously been reported (see Clapp, D. W., et al., Blood 78:1132-1139 (1991); Anderson, Science 288:627-9 (2000); andCavazzana-Calvo et al., Science 288:669-72 (2000)). The inventionfurther relates to transplantation methods, to introduce into a subjecta cell comprising a nucleic acid capable of encoding a KCC2, or tointroduce into a subject a cell which has been treated in vitro or exvivo with a compound capable of decreasing intracellular chloride levels(e.g. by culturing the cell in an appropriate medium comprising thecompound). In an embodiment, such a cell is a neural cell or a precursorthereof, e.g. a stem cell capable of developing/differentiating into aneural cell (neuron progenitor cell). Methods relating to neural stemcell isolation, proliferation, characterization and/or transplantationare described in for example U.S. Pat. Nos. 5,851,832; 5,968,829;5,411,883; 5,750,376; 6,040,180; 5,753,506 and 6,001,654. The nucleicacid may be present in a vector as described above, the vector beingintroduced into the cell in vitro, using for example the methodsdescribed above. In an embodiment, the cell is autologous, and isobtained from the subject. In embodiments, the cell is allogeneic orxenogeneic.

Given the correlation between intracellular chloride levels in a CNScell and pain, compounds which are capable of modulating, e.g.decreasing, intracellular chloride levels in a CNS cell can be used forthe prevention and treatment of pain. In an embodiment, compounds thatmodulate, e.g. increase or upregulate, chloride transporter, such asKCC2, activity/expression can be used for decreasing intracellularchloride levels and ultimately prevent or treat pain. Therefore, theinvention further relates to screening methods for the identificationand characterization of compounds capable of modulating intracellularchloride levels and/or chloride transporter activity and/or expression.Therefore, the invention further provides a method of determiningwhether a candidate compound is capable of modulating intracellularchloride levels in a cell, and in turn is useful for the prevention andtreatment of pain. In an embodiment, the method comprises contacting aCNS-derived cell with said candidate compound and determining whetherthe intracellular chloride level has decreased in the presence of thetest compound. A decrease in intracellular chloride level is indicativethat the test compound may be used for the treatment or the preventionof pain. As used herein, a “CNS-derived cell” is a cell isolated orderived from a CNS tissue, and in embodiments includes both primaryneuronal cultures, immortalized neuronal cell lines, as well as acceptedin vitro neuronal model systems (e.g. cells differentiated into neuronsin vitro). In an embodiment, the above-mentioned cell possesses achloride transporter or KCC2 activity. In yet a further embodiment, thecell endogenously expresses a chloride transporter (e.g. KCC2). In afurther embodiment the above-mentioned cell has been geneticallyengineered to express a chloride transporter gene or a KCC2 gene. In anembodiment, the cell may be an appropriate host cell comprising anexogenously introduced source of a chloride transporter, such as KCC2.Such a host cell may be prepared by the introduction of nucleic acidsequences encoding a chloride transporter or KCC2 into the host cell andproviding conditions for the expression of such nucleic acid. In anembodiment, such a nucleic acid is DNA. Such host cells may beeukaryotic, such as amphibian or mammalian cells. In an embodiment, suchhost cells are human.

The invention also provides another method for the identification orcharacterization of compounds useful for the treatment and prevention ofpain. In an embodiment, the method comprises contacting a CNS-derivedcell with the candidate compound and determining whether chloridetransporter activity has been modulated in the presence of the testcompound. A modulation, e.g. increase, in chloride transporter activityis indicative that the test compound may be used for the treatment orthe prevention of pain. In an embodiment, the chloride transporter isKCC2. KCC2 activity may be determined, for example, by measuringpotassium transport, chloride transport, intracellular chloride levelsand anion reversal potential.

The above-mentioned methods may be employed either with a single testcompound or a plurality or library (e.g. a combinatorial library) oftest compounds. In the latter case, synergistic effects provided bycombinations of compounds may also be identified and characterized. Theabove-mentioned compounds may be used for prevention and/or treatment ofpain, or may be used as lead compounds for the development and testingof additional compounds having improved specificity, efficacy and/orpharmacological (e.g. pharmacokinetic) properties. In an embodiment thecompound may be a prodrug which is altered into its active form at theappropriate site of action, e.g. in CNS tissue (e.g. in the spinalcord). In certain embodiments, one or a plurality of the steps of thescreening/testing methods of the invention may be automated.

As noted above, the invention further relates to methods for theidentification and characterization of compounds capable of modulating,in an embodiment increasing, chloride transporter, e.g. KCC2, geneexpression. Such a method may comprise assaying chloride transporter,e.g. KCC2, gene expression in the presence versus the absence of a testcompound. Such gene expression may be measured by detection of thecorresponding RNA or protein, or via the use of a suitable reporterconstruct comprising a transcriptional regulatory element(s) normallyassociated with such chloride transporter or KCC2 gene, operably-linkedto a reporter gene. A first nucleic acid sequence may “operably-linked”with a second nucleic acid sequence when the first nucleic acidsequence-is placed in a functional relationship with the second nucleicacid sequence. For instance, a promoter is operably-linked to a codingsequence if the promoter affects the transcription or expression of thecoding sequences. Generally, operably-linked DNA sequences arecontiguous and, where necessary to join two protein coding regions, inreading frame. However, since, for example, enhancers generally functionwhen separated from the promoters by several kilobases and intronicsequences may be of variable lengths, some polynucleotide elements maybe operably-linked but not contiguous. “Transcriptional regulatoryelement” is a generic term that refers to DNA sequences, such asinitiation and termination signals, enhancers, and promoters, splicingsignals, polyadenylation signals which induce or control transcriptionof protein coding sequences with which they are operably-linked. Theexpression of such a reporter gene may be measured on thetranscriptional or translational level, e.g. by the amount of RNA orprotein produced. RNA may be detected by for example Northern analysisor by the reverse transcriptase-polymerase chain reaction (RT-PCR)method (see for example Sambrook et al (1989) Molecular Cloning: ALaboratory Manual (second edition), Cold Spring Harbor Laboratory Press,Cold Spring Harbor, N.Y., USA). Protein levels may be detected eitherdirectly using affinity reagents (e.g. an antibody or fragment thereof[for methods, see for example Harlow, E. and Lane, D (1988) Antibodies:A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold SpringHarbor, N.Y.]; a ligand which binds the protein) or by other properties(e.g. fluorescence in the case of green fluorescent protein) or bymeasurement of the protein's activity, which may entail enzymaticactivity to produce a detectable product (e.g. with-alteredspectroscopic properties) or a detectable phenotype (e.g. alterations incell growth). Suitable reporter genes include but are not limited tochloramphenicol acetyltransferase, beta-D galactosidase, luciferase, orgreen fluorescent protein. In an embodiment, a candidate compound mayfurther be assayed to determine if it is capable of modulating achloride transporter-mediated process (e.g. KCC2-mediated process) orchloride transporter activity (e.g. KCC2 activity). In an embodiment,such chloride transporter-mediated process is ion transport, e.g.potassium or chloride transport, as determined by for example byassessing potassium and/or chloride levels (e.g. intracellularly) or bymeasuring anion reversal potential (electrophysiologically), membranepotential, for example as described in the examples below.

The invention also relates to the diagnosis and prognostication of pain.In an embodiment, the pain is caused by an alteration in ion, e.g. anionor chloride, homeostasis in the nervous system, e.g. central nervoussystem, of a subject. Without wishing to being bound to any particulartheory, a reduced capacity of potassium and chloride export from neuronsin the central nervous system (CNS) may lead to persistent neuronalhyperexcitability and ultimately pain.

The invention thus provides a method for diagnosing or prognosticatingpain associated with CNS dysfunction. As used herein, “CNS dysfunction”is an alteration in neuronal ionic homeostasis in the CNS. In anembodiment, the pain associated with such CNS dysfunction is neuropathicpain. In an embodiment, the method comprises determining anintracellular chloride level in a CNS neural cell and comparing thechloride level to a corresponding control level. In this particularmethod, an increase in the test level relative to a control level is anindication that the subject is experiencing pain associated with CNSdysfunction. In an embodiment, the method may comprise determiningwhether CNS chloride transporter activity or expression (e.g. KCC2activity or expression) is modulated, e.g. upregulated or increased,relative to a control activity or expression. In yet another embodiment,the control chloride level can be selected from an established standard,a corresponding chloride level determined in the subject at an earliertime; a corresponding chloride level determined in said subject when thesubject is experiencing less pain (relative to the current sensation ofpain noted above) or substantially no pain; or a corresponding chloridelevel determined in a control subject experiencing less pain (relativeto the current sensation of pain in the test subject noted above) orsubstantially no pain. In an embodiment, a subject or control subjectexperiencing less pain or substantially no pain presents no evidentlesions to his central or peripheral nervous system (e.g. neuropathicpain) or persistent pain. In yet another embodiment, the controlactivity or expression can be selected amongst an established standardof KCC2 activity or expression; a corresponding level of KCC2 activityor expression determined in the subject at an earlier time; acorresponding level of KCC2 activity or expression determined in thesubject when the subject is experiencing less pain (as above) orsubstantially no pain; or a corresponding level of KCC2 activity orexpression determined in a control subject experiencing less pain (asabove) or substantially no pain. In an embodiment, the KCC2 activity maybe determined as described above.

For example, intracellular chloride levels may be determined byadministering, to a subject, an indicator compound (such as a compoundindicative of chloride level) that is capable of contacting a CNS neuralcell of that subject. Following the administration of the indicatorcompound, assessment of the in vivo signal associated with suchindicator compound may be performed. In an embodiment, an indicatorcompound, such as a radionuclide (e.g. Thallium-201 (²⁰¹Tl),⁹⁹Tcm-tetrofosmin, ⁹⁹Tcm-MIBI or ^(99m)Tc-HMPAO or chloride conjugatesthereof) or a compound indicative of KCC2 expression (such as animmunodetection-based reagent (e.g. antibody, single chain antibody orFab fragment directed against the KCC2 polypeptide)) may be employed. Inyet another embodiment, the indicator compound, upon intravenousinjection, may cross the blood-brain-barrier and accumulate in neuronsof the CNS analogously to potassium, i.e. to reflect potassium levels.In another embodiment, the dose of such radionuclide (e.g. ²⁰¹Tl) may beabout 100 MBq (3 mCi). In yet another embodiment, the radionuclide (e.g.²⁰¹Tl) may be injected 15-20 minutes prior to SPECT imaging. Followinginjection of the indicator compound, an imaging technique may beperformed to assess the in vivo signal associated with the indicatorcompound. Such imaging techniques include, but are not limited to,single photon emission computed tomography (SPECT), positron emissiontomography and/or magnetic resonance imaging. The imaging technique mayenable the assessment of the in vivo signal of the indicator compound,such as the neural potassium gradient. Images can be obtained, forexample, using gamma camera equipped with a high-resolution (5-7 mm)collimator and interfaced with a dedicated computer system. In anembodiment, serial projection images can be aquired over a 180° arc. Inyet another embodiment, the radionuclide (e.g. ²⁰¹Tl) retention byneurons can be expressed as a retention index (RI). The “retentionindex” as described herein is defined as:

$\frac{{{Delayed}\mspace{14mu}{retention}} - {{early}\mspace{14mu}{retention}}}{{Early}\mspace{14mu}{retention}} \times 100$

In an embodiment, the “retention” of the retention index is hereindefined as the amount of indicator compound (e.g. tracer orradionuclide) retained by a specific tissue at a certain time. In afurther embodiment, the early retention is assessed before the delayedretention. In a further embodiment, the retention index is measured in aCNS tissue.

In an embodiment, the methods of diagnosis/prognostication noted abovemay be performed in conjunction with the therapeutic/prophylacticmethods noted above, for preventing or treating pain associated with CNSdysfunction in a subject. Such a method thus comprises the diagnosis orprognostication of pain associated with CNS dysfunction and, inaccordance with the diagnosis/prognosis, decreasing intracellularchloride levels in a CNS cell of the subject thereby to prevent or treatpain.

Although various embodiments of the invention are disclosed herein, manyadaptations and modifications may be made within the scope of theinvention in accordance with the common general knowledge of thoseskilled in this art. Such modifications include the substitution ofknown equivalents for any aspect of the invention in order to achievethe same result in substantially the same way Numeric ranges areinclusive of the numbers defining the range. In the claims, the word“comprising” is used as an open-ended term, substantially equivalent tothe phrase “including, but not limited to”. The following examples areillustrative of various aspects of the invention, and do not limit thebroad aspects of the invention as disclosed herein.

Throughout this application, various references are referred to describemore fully the state of the art to which this invention pertains. Thedisclosures of these references are hereby incorporated by referenceinto the present disclosure.

EXAMPLES Example 1 Methods

Nerve Injury. Briefly, peripheral nerve injury was induced by surgicallyimplanting a polyethylene cuff (˜2 mm long, 0.7 mm inner diameter)around the sciatic nerve of adult, male, Spague-Dawley rats aspreviously described (16). A group of rats also received sham surgery.Only animals that showed a gradual decrease in mechanical threshold(over 14-17 days) down to 2.0 g or less were used for furtherexperiments.

Behavioural Testing. Thermal and mechanical threshold for nociceptivewithdrawal reflexes were tested as previously described (17).

Slice preparation. Parasagittal slices (300-350 μm) of spinal cord wereprepared from adult (>50 days old) male rats as previously described(9). Slices were continually superfused (2-3 ml·min⁻¹) with artificialcerebrospinal fluid (ACSF) containing (in mM): 126 NaCl, 26 NaHCO₃, 10glucose, 2.5 KCl, 2 CaCl₂, 2 MgCl₂, 1.25 NaH₂PO₄, 0.001 TTX (bubbledwith 95% O₂−5% CO₂, pH˜7.4); when measuring GABA_(A)/GlyR-mediatedcurrents, 10 μM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 40 μMD2-amino-5-phosphonovaleric acid (APV) were added to block fastglutamatergic transmission.

Recordings. For perforated patch recordings, the pipette tip was filledwith a solution containing (in mM): 130 cesium. gluconate (CsGluc), 5CsCl, 2 MgCl₂, 11 BAPTA Calcium chelator (buffer), 1 CaCl₂, 4 ATP, 0.4GTP, 10 HEPES (pH˜7.4). The pipette was back-filled with this samesolution supplemented with 25 μg/ml gramicidin D (gramicidin stock wasat 10 mg/ml in DMSO). Recordings in this mode were selected when accessresistance was stable between 25-45 MΩ. For whole-cell voltage-clamprecordings, pipettes were filled with the above solution withoutgramicidin D. Similarly, whole-cell current-clamp recordings wereperformed using pipettes filled with the same intracellular solution aswith voltage-clamp, except potassium methyl sulfate (KMeSO₄) was used toreplace CsGluc. To clamp E_(anion) at 0 mV, CsGluc was replaced with 110mM CsCl in the intracellular solution. All whole-cell recordings atE_(anion)=0 mV were made at Vm=−60 mV in the presence of GluR-blockers.GABA was applied locally for 30-250 ms by pressure ejection through apatch micropipette. Data acquisition and analysis of PSCs was performedas previously described (9). All measurements are given as means±SEM,except where indicated. Statistical significance was tested usingStudent's t-tests for comparison of mean values, chi-square tests forcontingency tables, and mixed design ANOVAs (post-hoc—Tukey's HSD) forrepeated measures.

Calcium Imaging. Slices were prepared from PNI and naïve rats asdetailed above for electrophysiological analysis. After 15 minincubation in ACSF, slices were loaded with 10 μM Fura-2-AM (afluorometric calcium indicator, AM=acetoxymethyl) in HEPES-bufferedsaline (+10% DMSO) for 1 hour. Slices were washed for ˜15 min with ACSFbefore being mounted in the recording chamber, where they continued tobe superfused by ACSF (2-3 ml·min⁻¹). [Ca²⁺]_(i) was fluorometricallymeasured using a Zeiss Axioscope equipped with epifluorescence optics.Images were acquired using a TILL Photonics monochromator coupled to aCCD camera and regions of interest (for ratioing) were drawn on clearlydistinct neuronal cell bodies.

Immunoblotting. Horizontal slices (150 μm) of the SDH were made from thelumbar enlargement of both PNI and naïve adult rats. Tissue extractswere prepared by homogenizing the slices with a Teflon pestle in abuffer containing 0.32 M sucrose, 0.5 mM Tris-HCl, pH 7.5, 2 mMethylenediaminetetracetic acid (EDTA), 2.5 mM β-mercaptoethanol, and acocktail of protease inhibitors (CompIete™, Roche Diagnostics).Supernatants from 3,000 g (20 min) and 10,000 g (30 min) centrifugationswere collected. Equal amounts of proteins (20 μg/lane) diluted in samplebuffer were preheated at 37° C. for 30 min, resolved by SDS-PAGE, andelectroblotted onto nitrocellulose membranes. Membranes were blocked 30min in 5% nonfat dry milk in TBST buffer (150 mM NaCl, 10 mM Tris-HCl,pH 7.4, 0.05% Tween-20) and incubated overnight at 4° C. with a rabbitanti-KCC2 antibody (1:1000, Upstate Biotechnology). After several washesin TBST, membranes were incubated for 30 min at room temperature withperoxidase-labeled goat anti-rabbit antibody (1:2000). Chemiluminescentbands were detected using Super Signal Femto™ (Pierce Biotechnology).Digital images were captured with the VersaDoc™ imaging system (BioRad)and data were analysed with Quantity One™ software (BioRad).

Oligodeoxynucleotides. KCC2 antisense and scrambledoligodeoxynucleotides, phosphorothioated at all positions were designedas previously described (18): antisense, 5′-TCTCCTTGGGATTGCCGTCA-3′ (SEQID NO: 7; +59 relative to the ATG starting signal); scrambled,5′-TCTTCTTGAGACTGCAGTCA-3′ (SEQ ID NO: 8).

Intrathecal Injections. At least three days prior to drugadministration, rats were anaesthetized with sodium pentobarbital (65 mgkg⁻¹) and a lumbar spinal catheter was inserted into the intrathecalspace, as previously described (11). Briefly, a small opening wascreated at the cisterna magna, and a catheter was inserted into thesubarachnoid space and caudally directed ˜8 cm to the lumbar enlargementof the spinal cord. Upon recovery from surgery, lower body paralysis wasinduced via i.t. (intrathecal) lidocaine (2%, 30 μl) injection toconfirm proper catheter localization. Only animals exhibitingappropriate, transient paralysis to lidocaine, as well a lack of motordeficits were used for behavioural testing. Following drug/vehicleadministration, animals were sacrificed and their vertebral columndissected to visually confirm correct placement of the catheter. Drugsincluded DIOA (10-30 μg, in 0.9% NaCl, 10% DMSO) andoligodeoxynucleotides (single doses of 2 μg at 0 h, 12 h & 24 h; 0.9%NaCl). Behavioural testing was performed as above; normal (˜15 g)mechanical threshold for withdrawal responses was confirmed in naïverats prior to receiving drug or vehicle. At the doses used, none of thecompounds produced motor disturbances or sedation as assessed bygrasping, righting and placing reflexes and behavioral observations(17).

Computer simulations. (see FIG. 5) All simulations were performed-withNEURON 4.3.1 using a compartment model of a generic spinal lamina Ifusiform neuron with morphology and passive membrane properties based on(19). Dendrites bifurcated up to fourth order and an axon similar tothat described in (19) were attached to the soma. Fast Na⁺ and delayedrectifier K⁺ currents based on (30) were inserted at 0.1 and 0.01 S/cm²,respectively, in the soma and axon initial segment and nodes; voltagethreshold for spiking was −49 mV. Two sets of inhibitory synapses weredistributed randomly in the perisomatic region and four sets ofexcitatory synapses were more distal; each set was driven by anindependent Poisson process at rates extrapolated from (31) and (32).

Electron microscopy. (see FIG. 6) Tissue was prepared forultrastructural analysis as previously described (35). Briefly, ratswere perfused through the aortic arch with 0.9% NaCl followed by afixative solution containing 4% paraformaldehyde (Sigma-Aldrich,Germany). After perfusion, spinal cords were removed, coronal blockswere dissected, then 60 μm thin sections were cut cryoprotected andfreeze-thawed over liquid nitrogen and rinsed several times in phosphatebuffer before incubation in the primary antiserum. After incubation inblocking solution containing 2% bovine serum albumin (BSA), sectionswere incubated in rabbit anti-KCC2 (1:500, Upstate Biotechnology, USA)for 48 hours at 4° C. After extensive washing, sections were incubatedwith 1 nm gold-conjugated anti-rabbit secondary antibody (1:250, Aurion)for 12 hours at 4° C. followed by silver intensification (SE-EM,Aurion). Sections were treated with 0.5% OsO₄ (20 min), dehydrated ingraded ethanol, then in propylene oxide and embedded in Durcupan ACM(Fluka). After ultra-sectioning (Ultracut™ UCT, Leica, Germany),specimens were examined using an electron microscope (Philips Tecnai 12,equipped with MegaView™ CCD camera). Non-consecutive (spacing>3 μm)ultrathin sections were analyzed in the electron microscope. Boutonswith synaptic profiles were randomly selected and analyzed in laminae I& II and white matter for the expression of the KCC2 protein (36).

Intrathecal administration of K-252a. (see FIG. 8) K-252a was preparedin 25 ul of 0.9% NaCl solution containing 10% DMSO. Intrathecalcatheterization was performed by creating a small opening at thecisterna magna, and inserting P10 polyethylene tubing into thesubarachnoid space—caudally directed ˜8 cm to the lumbar enlargement ofthe spinal cord.

Example 2 Results

Peripheral neuropathy was induced in rats by chronically constrictingthe sciatic nerve (FIG. 1 a). To test whether the hyperexcitability(sensitization) of SDH neurons that follows peripheral nerve injury(PNI) is associated with modification of the anion gradient (∇_(anion)),anion reversal potential (E_(anion)) was measured usinggramicidin-perforated patch clamp recording. This technique avoidsdisrupting the intracellular anion concentration (8). Responses toexogenous GABA application showed that the anion reversal potential(E_(anion)) of lamina I (LI) neurons taken from PNI rats was −49.0±2.3mV (range: −40 to −62.2 mV, n=9) compared to −72.6±3.5 mV (range: −63.0to −79.9 mV, n=5; p<0.005) in LI neurons from naïve rats (FIG. 1 b-d).Resting membrane potential was not significantly different between PNI(−62±4 mV, n=7) and naïve rat LI neurons (−61±2 mV, n=16; p>0.1).Spontaneous and evoked postsynaptic currents (PSCs), recorded from PNIrat LI neurons in the presence of fast glutamate receptor (GluR)blockers were also inward (depolarizing from rest), their mean reversalpotential increasing by 16.1 mV relative to that in lamina I neuronsfrom naïve rats (n=6, PNI; n=4, naïve). It was then investigated whetherother properties of synaptic transmission were altered in the SDH afterPNI. Inhibitory miniature PSCs (mPSCs) in LI neurons from naïve rats aremediated by glycine receptors (GlyRs) alone despite GABA and glycinecorelease from local inhibitory interneurons (9; FIG. 2 a). WhileGluR-mediated mPSCs were unaffected by PNI (FIG. 2 b), in all cellstested from PNI rats, a population of outward mPSCs at 0 mV persisted inthe presence of the GlyR antagonist strychnine (up to 1 μm; n=4). Theseremaining mPSCs were mediated by GABA_(A)R_(S), as they were blocked bybicuculline (10 μM) and displayed prolonged decay kinetics compared tothe GlyR-mediated component (τ_(D(GABA) _(A) _(R))=34.0±2.9 ms, n=5, vs.τ_(D(GLyR))=11.3±1.3 ms, n=6; p<0.01; FIG. 2C).

Kinetic analysis further revealed that the decay phase of 36.9±2.3% ofmPSCs followed a dual exponential function (τ_(D1)=7.5±2.0 ms andτ_(D2)=51.3±7.9 ms; n=6; FIG. 2 c). These events possessed both aGABA_(A)R and a GlyR-mediated component, as either strychnine orbicuculline could lead to the abolition of their respective components(n=4). Therefore, in parallel with the collapsed ∇_(anion), PNI causedreorganization at LI synapses thereby unmasking GABA_(A)R-only and-mixedGABA_(A)R/GlyR-mediated mPSCs, in addition to those mediated by GlyRsalone. This synaptic organization is similar to that observed inimmature LI-II neurons (9). The net effect of this synaptic switch isthat it yielded a population of quantal synaptic events withsignificantly longer decay kinetics.

To examine the function of the PNI-induced GABA_(A)R-mediatedcontribution to mPSCs, we analysed both the peak conductance and thefrequency of mPSCs. This was performed using CsCl-filled pipettes toclamp the E_(anion) at 0 mV in both LI neurons taken from PNI and naïverats to prevent biased detection of mPSCs resulting from changes indriving force. Peak conductance of GlyR-only mPSCs recorded in LIneurons taken from PNI rats was significantly smaller (˜2-fold) thanthat recorded from naïve rat LI neurons (FIG. 2 d). The addition ofGABA_(A)R-mediated events in the PNI condition, however, partiallycompensated the decrease in GlyR-only conductance. The peak conductanceof GluR-mediated quantal events was not significantly different betweenLI neurons taken from naïve and PNI rats (FIG. 2 d).

Factoring together the changes in peak conductance, kinetics, anddriving force, the net charge carried by GlyR-only mPSCs at restingmembrane potential in LI neurons taken from PNI rats was nearly 3-foldsmaller than that in naive rats (FIG. 2 e). With the contribution ofGABA_(A)Rs, however, the net charge carried by mPSCs in PNI rats roseback to that mediated by GlyRs in naïve rats. This result suggests that,although equivalent in magnitude, hyperpolarizing charge in naïve LIneurons was carried by GlyR-mediated mPSCs alone, whereas depolarizingcharge was transferred predominantly via GABA_(A)Rs in PNI rat LIneurons, due to the prolonged decay kinetics of GABA_(A)R-mediatedmPSCs.

The frequency of GlyR-only mPSCs recorded in LI neurons from PNI ratswas observed to be significantly less (0.13±0.04 Hz, n=5) than that forGlyR-only mPSCs in naive rat LI neurons (0.18±0.04 Hz, n=6; p<0.05; FIG.2 f). As with peak conductance, however, the addition of theGABA_(A)R-mediated mPSCs compensated the PNI-induced decrease infrequency (0.22±0.10 Hz, n=4, for all GABA_(A)R and/or GlyR-mediatedevents combined; p>0.5). In contrast, there was no significant change inthe frequency of GluR-mediated events in LI neurons isolated from PNIrats (1.51±0.90 Hz, n=9) compared to LI neurons from naïve rats(0.82±0.40 Hz, n=S; p>0.3; FIG. 2 f).

If depolarizing GABA_(A)R/GlyR-mediated postsynaptic currents exert anet excitatory influence in PNI LI neurons, they should directly evokeaction potentials, and consequently lead to Ca²⁺ influx. To test thishypothesis, we employed Ca²⁺-imaging using fura-2-am loaded LI neuronsin slice to obtain a large data set. Administration of exogenous GABA toneuronal somata caused a significant increase in the concentration ofintracellular Ca²⁺ ([Ca²⁺]_(i)) in 19% of LI neurons (n=53; FIG. 3 a,c)lying ipsilateral to the site of PNI. This represents a seven-foldincrease compared to LI neurons found in naïve and/or contralateraldorsal horn, where an increase in [Ca²⁺]_(i) to GABA application wasobserved in only 1 of 37 neurons tested (FIG. 3 b,c). These responseswere blocked by bicuculline (10 μM; n=5) and by the voltage sensitivesodium channel blocker tetrodotoxin (TTX; 1 μM; n=31). We then furtherconfirmed electrophysiologically that applied GABA and synapticallyelicited anionic postsynaptic potentials can directly evoke actionpotentials (FIG. 3 d,e). These results indicate that postsynaptic anionfluxes can cause net excitation in lamina I neurons in PNI rats. We thencompared KCC2 protein levels by immunoblotting on horizontal slices ofSDH. The KCC2 expression level in the lumbar SDH ipsilateral to the PNIwas significantly reduced (>2-fold) relative to the side contralateralto the injury (FIG. 3 f). In naïve rats, there was no significantdifference between the two sides (n=3).

If a decrease in the expression of the KCC2 exporter leads to anincrease in neuronal [Cl⁻]_(i) and, in turn, GABA_(A)R-mediateddepolarization, a pharmacological blockade of the KCC2 exporter in LIneurons from naïve rats should have the same effect. To test for thispossibility, we bath applied the selective KCC2 blocker DIOA (30 μM) tonaïve spinal slices. As in the PNI condition, GABA application in thepresence of DIOA caused an increase in [Ca²⁺]_(i) in 30% of naïve LIneurons tested (FIG. 3 b,c).

To assess whether the empirically determined changes inGABA_(A)R/GlyR-mediated postsynaptic control were sufficient to accountfor the central sensitization which follows PNI, we simulated in vivoconditions using a biophysically-realistic neuron model (FIG. 5). Thesimulation confirmed that, after PNI, the extent of LI neuronalsensitization varied as a function of their E_(anion), ranging fromslight disinhibition to a net hyperexcitation.

To test whether this hyperexcitability (sensitization) would result in adecrease in the stimulus threshold to evoke a nociceptive withdrawalreflex, we administered DIOA (15-30 μg) directly to the lumbarenlargement of the spinal cord in intact rats via an intrathecalcatheter. DIOA caused a rapid and reversible decrease in nociceptivethreshold to both mechanical and thermal stimuli (FIG. 4 a-b). A similardecrease in nociceptive threshold was further obtained via selectiveknock-down of the exporter using spinal administration of an antisenseoligodeoxynucleotide against KCC2 mRNA (FIG. 4 e), further confirmingthe functional impact of KCC2 dowregulation.

As shown in FIG. 7, we demonstrate that in lamina I neurons taken fromrats with peripheral neuropathy, the transmembrane anion reversalpotential (E_(anion)) is significantly more depolarized than that inlamina I neurons taken from naïve rats. The anion (bicarbonate andchloride) reversal potential (E_(anion)) of recorded from lamina Ineurons taken from naïve rats was significantly less than that recordedfrom the lamina I neurons of rats that had received a peripheral nerveinjury (PNI). Bath application of both BDNF (50 ng/ml; N/BDNF) and NGF(50 ng/ml; N/NGF) caused the E_(anion) recorded from naïve rat lamina Ineurons to become significantly depolarized, indicating a collapse ofthe transmembrane anion gradient. Alternatively, bath application of theTrkB antagonist K-252a (200 nM; P/K252a) to lamina I neurons taken froma PNI rat caused a hyperpolarization of the E_(anion) to a level similarto that observed in lamina I neurons taken from naïve rats. AllE_(anion) values were confirmed using gramicidin-D perforated-patchvoltage-clamp recordings. This depolarized E_(anion) is the result of adecreased expression of the KCC2 cotransporter in the lamina I neuronstaken from neuropathic rats, as noted above. In lamina I neurons fromnaïve rats, it is further shown herein that the E_(anion) may bedepolarized significantly via the perfusion of the growth factors NGFand BDNF, suggesting that these growth factors may decrease the functionand/or expression of the KCC2 protein in the superficial dorsal horn.Alternatively, blocking the BDNF receptor, TrkB, in lamina I neuronstaken from neuropathic rats using the protein kinase inihibitor K-252a,is shown herein to reverse the depolarization of the E_(anion),returning this value to a level similar to that observed in lamina Ineurons taken from naïve rats. Further, as shown in FIG. 8, intrathecaladministration of the receptor tyrosine kinase inhibitor K-252a (6 nM)(but not vehicle injection alone) resulted in an increase in thethreshold for tactile nociceptive withdrawal in rats that had receivedperipheral nerve injury. K-252a can thus reverse thehyperalgesia/allodynia after its development following peripheral nerveinjury. K-252a did not produce any motor disturbances or sedation asassessed by grasping, righting and placing reflexes and behavioralobservations. It is envisioned that this inhibitor reactivates the KCC2cotransporter in lamina I neurons taken from neuropathic rats byblocking phosphorylation, perhaps at a protein tyrosine kinase site onthe transporter or on its transcription factors (or other regulatorysubstrate).

The results herein show that the painful neuropathy that follows PNI canbe explained by a downregulation of the KCC2 exporter and the resultantshift in the ∇_(anion) in spinal LI neurons. They also demonstrate thatsuch a modification of ∇_(anion) in adult animals can occur in a neurontranssynaptic to an injury site. Previous efforts to identify asubstrate underlying the hyperexcitability characteristic of peripheralneuropathy have focussed on measuring changes in number of GABAergicinterneurons, GABA content or GABA_(A)R expression. The results havebeen contradictory (3-6). The findings presented herein provide a newavenue to understand such mechanisms of disinhibition. The conversion ofthe GABA_(A)R/GlyR-mediated postsynaptic action via a shift in ∇_(anion)provides a mechanistic basis for central sensitization, includingincreases in neuronal responsiveness and number of excitatory inputs.

A critical feature of the spinal cord is that it employs two verydistinct GABAergic inhibitory mechanisms: GABAergic control of thecentral terminals of sensory fibres already involves a depolarizingmechanism (39), in contrast to dorsal horn cells where GABAergicinhibition involves hyperpolarization. Thus, the change in KCC2expression reported here affects the polarity of GABA action in only oneof the two inhibitory mechanisms controlling sensory input. This isconfirmed by the fact that primary afferents lack expression of KCC2(FIG. 4 f, g; see also FIG. 6). GABA/glycine-mediated depolarization mayalso serve as a gating mechanism to enable excitation via voltagesensitive Ca²⁺ channels (VSCCs) and NMDA receptor/channels (10). Ca²⁺influx via these channels is thought to be critical for thesensitization of spinal neurons (11). Indeed, blocking these Ca²⁺channels in humans by drugs such as gabapentin and ketamine has provenhighly efficacious in the treatment of neuropathic pain (12-14).However, use of Ca²⁺ channel blockers, particularly ketamine and otherNMDA antagonists, is associated with many undesirable side effects (14,15).

Example 3 In Vitro TrkB-Dependent Modulation of KCC2

Parasaggital slices (250-300 microm) were made from the dorsal horn ofnaïve rats or PNI rats. Slices were continually perfused with anoxygenated Ringer's solution and were permitted to equilibrate for atleast 1.5 hours prior to manipulation. Unless otherwise specified,slices were further perfused with 10 microM CNQX, a blocker of non-NMDAionotropic glutamate receptors. Recordings were made fromvisually-identified lamina I neurons using gramicidin-D perforated-patchor whole-cell voltage-clamp recordings. In both cases, pipettes werefilled with an intracellular solution containing either potassium methylsulphate or cesium gluconate as the major ionic species. E_(anion) wasmeasured by applying a series of brief (5-10 ms) applications ofexogenous GABA to the soma of the neurons of interest; by manipulatingthe membrane potential of the neuron, the point at which GABA elicitedneither an inward nor an outward anion current was taken as E_(anion).All measurements of membrane potential were corrected for liquidjunction potential, pipette offset, and resistances.

As shown in FIG. 12, both brain-derived neurotrophic factor—(BDNF; 50ng/ml in bath) mediated activation of TrkB and nerve growthfactor-—(NGF; 50 ng/ml in bath) mediated activation of TrkA caused asignificant depolarization of the anion reversal potential (E_(anion))in lamina I neurons taken from naïve rats.

Using slices taken from peripheral nerve injured (PNI) rats, where theE_(anion) is chronically depolarized, application of various inhibitorsof components of an intracellular pathway coupled to TrkB receptors wereshown to cause a significant hyperpolarization of the E_(anion)(bicarbonate and chloride), to levels similar to that observed in slicestaken from naïve rats (FIG. 13). Agents that rendered this effectincluded, but are not limited to, an antibody directed against TrkB,(anti-TrkB-IgG 1 μg/ml in bath); K-252a, an inhibitor of TrkA/Bautophosphorylation (200 nM in bath); H-89, a membrane-permeableinhibitor of cyclic AMP-dependent kinase (PKA); 15 μM in bath); andKN-93, a membrane permeable inhibitor of calmodulin-dependent kinase IIand IV (5 μM in bath).

Example 4 TrkB-Dependent Modulation of Nociceptive Threshold In Vivo

All drugs used for local spinal delivery via intrathecal catheter weredissolved in 0.9% NaCl with or without 10% v/v DMSO. Intrathecalcatheterization was performed by creating a small opening at thecisterna magna, and inserting a short P10 polyethylene tube into thesubarachnoid space, caudally directed ˜8 cm to the lumbar enlargement(L4-5) of the spinal cord. No drug administered produced motordisturbances or sedation, as assessed via analysis of grasping, rightingand placing reflexes and other behavioral observations. Von Frey testingwas used to assess the 50% withdrawal threshold to mechanicalstimulation as previously described (41). All experiments were performedon intact, adult Sprague-Dawley rats.

Local spinal delivery of various agents using an intrathecal catheterled to the identification of several compounds that either effect areduction of nociceptive threshold for tactile stimulation in naïverats, or raise the nociceptive threshold in PNI rats.

Local spinal delivery of either an adenovirus transducing BDNF (FIG. 14)or human recombinant BDNF (10 μg/day×6 days), but not of an adenovirustransducing the green-fluorescent protein, caused a significant decreasein the nociceptive threshold for mechanical stimulation in naïve rats.Likewise, intrathecal delivery of human recombinant NGF (FIG. 15; 10μg/day×6 days) to naïve rats caused a very similar decrease in the saidnociceptive threshold.

On the other hand, serial administration of antibody directed againstTrkB (anti-TrkB-IgG 12 μg/2 hrs×3) via intrathecal catheter to PNI ratseffected a significant increase in nociceptive threshold to mechanicalstimulation (FIG. 16). Local spinal delivery of the PKA inhibitor H-89(380 nmol) also caused an increase in the nociceptive threshold (FIG.17).

Throughout this application, various references are cited, whichdescribe more fully the state of the art to which this inventionpertains. The disclosures of these references are hereby incorporated byreference into the present disclosure.

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1. A method of identifying a compound for treatment of pain, said methodcomprising: (a) contacting a test compound with a cell expressing a CNSchloride transporter; (b) comparing an intracellular chloride level ofsaid cell in the presence of the test compound with an intracellularchloride level of said cell in the absence of said test compound;wherein a decrease in the level of intracellular chloride in thepresence relative to in the absence of said test compound is anindication that said test compound may be used for treatment of pain. 2.The method of claim 1, wherein said pain is selected from the groupconsisting of chronic inflammatory pain, pain associated with arthritis,fibromyalgia, back pain, cancer-associated pain, pain associated withdigestive disease, pain associated with Crohn's disease, pain associatedwith autoimmune disease, pain associated with endocrine disease, painassociated with diabetic neuropathy, phantom limb pain, spontaneouspain, chronic post-surgical pain, chronic temporomandibular pain,causalgia, post-herpetic neuralgia, AIDS-related pain, complex regionalpain syndromes type I and II, trigeminal neuralgia, chronic back pain,pain associated with spinal cord injury and recurrent acute pain.
 3. Themethod of claim 1, wherein said chloride transporter isK⁺-Cl⁻cotransporter 2 (KCC2).
 4. The method of claim 1, wherein saidintracellular chloride levels is determined by measuring anion reversalpotential.